Extremely hazardous substances (EHSs) that are in solid form are subject to one of two different threshold planning quantities (TPQs), a lower level or 10,000 pounds (40 CFR 355.15). Why does the list of EHSs only have one TPQ for certain solids, such as sodium cyanide? If a facility has sodium cyanide in a non-powder, non-molten, non-solution form, can the facility use the 10,000 pound TPQ?
For EHSs that are in solid form, the lower TPQ applies only if it is a powder with a particle size less than 100 microns; is in solution; is in molten form; or has a National Fire Protection Association rating of 2, 3, or 4 for reactivity. If the solid does not meet these specific criteria, the TPQ will default to 10,000 pounds. EPA has identified reactive solids, such as sodium cyanide, on the list of EHSs in Part 355, Appendix A with an “a” in the notes column. For these substances, the TPQ does not default to 10,000 pounds for non-powder, non-molten, non-solution form.